In a formation of a semiconductor including a plurality of layers, the layers have to be electrically isolated from each other, but at the same time the layers have to be electrically connected to each other in a necessary region. For this, each layer may be electrically isolated from each other by an interlayer insulating layer and may be electrically connected to each other by conductor connecting the layers. In a formation of the conductor, a study for obtaining process margin and/or process efficiency is being performed.